The freshness filter appears to filter out many pages that should be included. For example, see this search:
https://api.cognitive.microsoft.com/bing/v5.0/search?q=iphone site:allentown.craigslist.org&count=10&offset=0&mkt=en-us&safesearch=Moderate&freshness=week

This can of course be tested in the console: https://dev.cognitive.microsoft.com/docs/services/56b43eeccf5ff8098cef3807/operations/56b4447dcf5ff8098cef380d/console

There are no results. However, if you remove the freshness=week portion, there are many results even just on the first page that are newer than one week old.

The extent of the missing results makes the freshness filter almost useless unfortunately.